1. Field of Invention
The field of the currently claimed embodiments of this invention relates to robotic systems, and more particularly to cooperative-control robots and systems.
2. Discussion of Related Art
Many surgical disciplines such as ophthalmology, otology, laryngology, neurosurgery, and cosmetic and reconstructive surgery, as well as non-surgical fields such as bio-medical research and micro assembly, have a micro manipulation component that pushes human sensory-motor limits. Several robotic solutions have been proposed to solve similar problems in surgery, most prominently the daVinci surgical robot from Intuitive surgical (FIG. 1). The daVinci robot was primarily designed for minimally invasive surgery, and uses a teleoperation control paradigm. This means that the control console and the robot itself are separate pieces of equipment, and the surgeon sits away from the patient.
Though the teleoperation paradigm presents many advantages in minimally invasive surgery, it presents little benefit in many microsurgical tasks. Separating the robot and console causes the whole system to have a much larger operating room (OR) footprint, and unnaturally removes the surgeon from the operation area. The overall bulk of the system makes it time consuming to set up and disengage, so it is difficult to bring it in and out of the OR as needed. Also, since the daVinci robot is designed to mimic the natural hand position of surgeons performing minimally invasive surgery, it has difficulty operating with instrument shafts parallel to each other, as in laryngeal surgery. These limitations can also result in the need to completely change surgical practices in order to accommodate the robot. Another major drawback of this system is its cost. The daVinci robot has both high fixed costs (initial robot cost ˜$2 million) and high variable costs (custom disposable surgical instruments, surgical training for daVinci operations).
Since the daVinci robot is mostly used in minimally invasive surgery, it is designed to operate through small incisions. This requires its instruments to pivot about the point where they enter the patient, so as not to put forces on the incision. This is called a remote center of motion (RCM), since the tool is rotating about a point that is outside of the robot. The daVinci robot achieves two rotational degrees of freedom (tilt and roll) about a remote center of motion using a rotation stage and a cable mechanism (FIG. 2). It also has a translational degree of freedom to insert and withdraw tools along the tool axis. This translation mechanism is at the end of the arm, which adds significant bulk and prevents the robot from operating with two instruments parallel to each other and in close proximity (FIG. 3).
Another approach to overcoming human sensorimotor limitations in surgery has been taken by the JHU Eye Robot 2 (FIG. 4). This system uses a cooperative control paradigm where the surgeon sits with the patient and holds the surgical tool along with the robot. The robot senses the surgeon's pressure on the tool through a force sensor and moves accordingly. This system is much smaller and requires less modification to surgical procedures than the daVinci robot.
The JHU Eye Robot 2 uses three translation stages to give x, y, and z translational degrees of freedom, as well as a rotation stage and a remote center of motion linkage2 to provide the necessary rotational degrees of freedom. If the tool needs to rotate about a point that is different from the rotation center of the mechanisms, then the translation stages can compensate and allow the tool's shaft to rotate about another point. The main limitation of this design is that it relies on a fundamentally serial mechanism, which requires each actuator to carry all subsequent actuators. This makes the overall system larger and heavier than it would otherwise need to be. The weight of the robot imposes speed limits on the translation stages, which in turn prevents them from tracking fast surgical motions, or compensating for centers of motion that are far from that of the mechanism.
An earlier version of the JHU Eye Robot 2, the JHU Eye Robot 1, used a standard 4-bar linkage rather than the remote center of motion linkage, a rotation stage, and a similar 3 degree of freedom (dof) set of translation stages (FIG. 5). The mechanism has no natural RCM point, and uses the translation stages to augment the rotation joints and provide RCM functionality. The RCM linkage was added in the JHU Eye Robot 2 because the translation stages in the serial design were too slow to compensate for the RCM point needed in eye surgery.
Alternative mechanisms for providing three degree of freedom translational motion exist, most notably the delta mechanism (FIG. 6). This mechanism uses three parallelogram linkages in parallel to provide x, y, and z translational degrees of freedom, as well as an extending shaft with two universal joints to provide an additional rotational degree of freedom, for a total of four degrees of freedom. An advantage of this mechanism is that the actuators act in parallel, meaning that they do not need to carry each other's mass. Because of this, the delta mechanism has been used extensively in industrial robotics for high-speed pick and place applications, as well as for surgical applications, and haptic master control (FIG. 7).
The delta mechanism has been used in surgical applications, most notably in maxillofacial surgery (FIG. 8).6 This system, the ISIS Surgiscope, is a large overhead delta robot designed to manipulate a surgical microscope, which was modified to manipulate surgical tools such as bone drills. It uses a force sensor to detect interaction forces between tools and tissue. Rather than a cooperative control paradigm, this system uses an “interactive planning, programming and teaching” scheme where the robot's freedom is restricted using limits on position, orientation, force, and torque. This system uses motors mounted on the delta robot's mobile platform ((8) in FIG. 6) to control the surgical tools.
This system is not well suited to microsurgery, due to its large size and mass. Also, since it is so large and ceiling mounted, it would not be feasible for two such systems to work together in a bimanual operation. The largely planned and pre-determined operating method this system uses would not be useful in surgeries without extensive preoperative imaging, registration, and rigid anatomy.
The delta mechanism has also been modified to integrate additional actuators into the arms of the system for the purpose of powering additional degrees of freedom at the tip (FIG. 9).7 A variant of the delta robot which uses linear actuators was also proposed in the original delta robot (FIG. 10). There thus remains the need for improved robots and robotic systems.